When searching and reconnoitering an area, multi-robots are more efficient than a single robot in view of time and space efficiency and stability against robot malfunctions. Researches are conducted on collaboration of the multi-robots, based on a centralized approach and a decentralized approach.
The centralized approach considers each robot as a single control module and operates a total set of robots as one large system. The centralized approach provides an optimal operation solution. However, it is operationally difficult to obtain operation states of the robots, and calculations of a robot behavior determination algorithm exponentially rise as the number of the robots increases.
Meanwhile, the decentralized approach allows each robot to determine its own behavior in accordance with a situation to achieve a group goal. Although the decentralized approach cannot provide the optimal solution, it exhibits stability to achieve the ultimate goal even when some robots malfunction. In addition, the operation complexity is low even when the number of the robots increases, and it is possible to determine the behavior even when partial environment information and robot information are given. On these bases, the decentralized approach is considered as a practical solution in field applications under an atypical environment.
Based on communication between the robots, the decentralized approach is classified into an explicit communication method and an implicit communication method. While the former is less efficient than the latter, it can be applied to underwater or complicate environments where visibility of the communication is not ensured.
The decentralized approach, which can be applied to actual atypical external environments, is studied to increase productivity. As an example, a market-based approach aims to increase the productivity by reallocating tasks based on bidding and auction algorithms among the robots. Researches also handle a stick-pulling problem using the collaboration of two robots in an unknown area, or the collaboration problem of two or more robots. Still, those researches and studies do not greatly increase the productivity of the robot.